Another anecdote (or maybe data point?!): Typeform basically had all the initial growth of the product via a "Powered by" button that was shown in the bottom of each form generated. We did no marketing/sales except having that "Powered By" button shown for forms created by all non-paying users.

Since the "Powered By" button of each form was affected by the number of people visiting each form and some creating their own, leading to more views of the "Powered By" button, we called it "Viral Marketing" (maybe "Marketing" is the wrong word, don't remember exactly what we used to call it) where the growth of the platform funded more growth of the platform, inherently.

So +1 for the "Powered By" button, leads to tons of people discovering your product based on already using it for something. Users who want to white-label the usage of your product will also be ready to pay more to get rid of it, so not only a acquisition channel, also a way of affecting how you set pricing.